1. Field of the Invention
The present invention relates to a voice coil composed of a bobbin and a coil, and a speaker using the voice coil.
2. Description of the Related Art
In a dynamic speaker, a bobbin is vibrated by a change of a current flowing through a coil wound around a bobbin, and vibrations thus generated are transmitted to a diaphragm. Accordingly, as a material that forms the bobbin of the voice coil, it is preferable to select a material that easily transmits the vibrations to the diaphragm. For the conventional bobbin, various materials such as kraft, aluminum, aramid fiber and polyimide are used (for example, Japanese Unexamined Patent Application Laid-Open (Koukai) No. 2002-300697).
However, in the case of using the conventional material, for example, the kraft, though the kraft is lightweight, and a sound pressure thereof in a mid/treble range is high, strength of the bobbin falls short, and accordingly, a feeling of distortion in the treble range is sensed in some cases. Moreover, in the case of using the kraft, a sound propagation velocity is relatively slow. In the case of using the aluminum, the strength of the bobbin is enhanced and the sound propagation velocity is increased in comparison with the case of using the kraft. However, since magnetic damping is applied to the bobbin, sound articulation in a bass range is not very satisfactory in some cases. Moreover, since specific gravity of the aluminum is larger than that of the kraft, a sound pressure thereof in the mid/treble range is sometimes decreased.
In the case of using the aramid fiber, though the aramid fiber is preferable for the bass range since specific gravity thereof is large, the aramid fiber is unsuitable for full range and mid/treble speakers. Moreover, also in the case of using the polyimide, though it is necessary to reduce weight of the bobbin by thinning a thickness thereof since specific gravity of the polyimide is large, the strength of the bobbin falls short when the thickness is thinned, and accordingly, a treble resonance occurs in some cases.
As described above, each of the materials used heretofore has merits and demerits, and there have not been obtained yet a voice coil and a speaker, which use a material that has a high propagation velocity, is lightweight and strong, and is capable of transmitting the vibrations with high efficiency.